The present invention relates to non-invasive methods of medical examination of a patient. In particular, the present invention relates to an impedance-based method of determining the concentration of glucose in blood.
Some of the non-invasive methods of determining the concentration of glucose in blood are based on measuring total electrical resistance (impedance) or a component of the total resistance of a body part of a patient. For example, Russian patent 2073242 describes a method of indicating the level of sugar in blood based on the changes in the dielectric permeability of a finger placed in the electrical field. In another example, described in Russian patent 2088927, the determination of the glucose concentration in blood was accomplished by varying the reactive impedance of the oscillating circuits. In particular, the effect of a human being on the reactive impedance of the oscillating circuits plugged into the secondary circuits of the high frequency generator was measured and the concentration of sugar in blood was monitored based on the changes of the current in the secondary circuits. In yet another example, such as U.S. Pat. No. 5,792,668, the method comprises performing a spectral analysis of the high frequency radiation reflected from a or transmitted through a human body. The measured parameter in that method was a phase difference between the incoming radiation and either reflected or transmitted radiation, characteristic a component of the total resistance of a human body. In yet another example, a device described in a Russian Certificate for a Utility Model #9703, a determination of the glucose concentration in blood was based on measuring the total resistance of a part of a human body using two different frequencies, determining a capacitive component of the total resistance and then converting the determined value of the capacitive component into a level of glucose in the blood of a patient.
All the above-described methods have a common disadvantage in that the accuracy of the measurements of glucose in blood is inferior to that of the invasive methods. On the other hand, the invasive methods always require taking a blood sample, which is undesirable from the viewpoint of safety and convenience. The above-described methods are based on the determination of the total or reactive resistance (or the components of the resistance) of a part of a human body and are not very accurate.
It is therefore desirable to provide a simple and accurate non-invasive method of determining a glucose concentration in blood, which method will later become the basis for individual glucose test kits.